gh-153569: remove redundant reader counters

The reader stores two prefetched lines together with an index and count that only describe whether each slot is occupied. Its control flags also use full integers.

Use the chunk slots as their own occupancy state and keep reader control flags byte-sized. This removes bookkeeping without changing the read order or buffer ownership.

Author: pablogsal

Parser/tokenizer/reader.c

@@ -259,7 +259,6 @@ initialize_file(struct tok_state *tok)
     if (result != _PYTOK_READ_LINE) {
         return -1;
     }
-    reader->prefetched_count = 1;
     Py_ssize_t bom_len;
     _PyTok_EncodingResult detection = _PyTok_DetectEncoding(
         tok, &reader->prefetched_lines[0], NULL, 0, &bom_len);
@@ -277,16 +276,13 @@ initialize_file(struct tok_state *tok)
         reader->prefetched_lines[0].data = first;
         reader->prefetched_lines[0].ownership = _PYTOK_CHUNK_PYMEM;
         result = read_file_line(tok, &reader->prefetched_lines[1]);
-        if (result == _PYTOK_READ_LINE) {
-            reader->prefetched_count = 2;
-        }
-        else if (result == _PYTOK_READ_EOF) {
+        if (result == _PYTOK_READ_EOF) {
             reader->file_eof = 1;
         }
-        else {
+        else if (result != _PYTOK_READ_LINE) {
             return -1;
         }
-        _PyTok_Chunk *second = reader->prefetched_count == 2
+        _PyTok_Chunk *second = reader->prefetched_lines[1].data != NULL
             ? &reader->prefetched_lines[1] : NULL;
         detection = _PyTok_DetectEncoding(
             tok, &reader->prefetched_lines[0], second, 1, &bom_len);
@@ -356,10 +352,13 @@ next_file(struct tok_state *tok, _PyTok_Chunk *chunk)
             return _PYTOK_READ_LINE;
         }
         _PyTok_Chunk input = {0};
-        if (reader->prefetched_index < reader->prefetched_count) {
-            input = reader->prefetched_lines[reader->prefetched_index];
-            reader->prefetched_lines[reader->prefetched_index++] =
-                (_PyTok_Chunk){0};
+        if (reader->prefetched_lines[0].data != NULL) {
+            input = reader->prefetched_lines[0];
+            reader->prefetched_lines[0] = (_PyTok_Chunk){0};
+        }
+        else if (reader->prefetched_lines[1].data != NULL) {
+            input = reader->prefetched_lines[1];
+            reader->prefetched_lines[1] = (_PyTok_Chunk){0};
         }
         else if (!reader->file_eof) {
             _PyTok_ReadResult result = read_file_line(tok, &input);

Parser/tokenizer/reader_internal.h

@@ -39,7 +39,6 @@ typedef struct {
 } _PyTok_Chunk;
 
 typedef struct _PyTok_Reader {
-    _PyTok_ReaderKind kind;
     PyObject *readline;
     PyObject *decoder;
     const char *prompt;
@@ -50,19 +49,17 @@ typedef struct _PyTok_Reader {
     char *file_buffer;
     Py_ssize_t file_buffer_cap;
     _PyTok_Chunk prefetched_lines[2];
-    int prefetched_index;
-    int prefetched_count;
 
     char *decoded;
     Py_ssize_t decoded_pos;
     Py_ssize_t decoded_len;
     Py_ssize_t decoded_cap;
-    int decoded_tail_is_implicit;
-
-    int file_initialized;
-    int file_eof;
-    int decoder_finalized;
-    int stop_interactive;
+    _PyTok_ReaderKind kind;
+    unsigned char decoded_tail_is_implicit;
+    unsigned char file_initialized;
+    unsigned char file_eof;
+    unsigned char decoder_finalized;
+    unsigned char stop_interactive;
 } _PyTok_Reader;
 
 struct tok_state;